“If you are looking for a cheap furnished room then here you have it,” the resident wrote, adding, “[Two] month rent required to move in. First come first served.”

Under NYCHA rules, only residents authorized by the agency may live in the apartments. Residents who violate the rules will be given an administrative hearing or taken to Housing Court.

Last year, Manhattan resident Sherman Gamble was charged with theft of public funds after impersonating his cousin — an NYCHA tenant who moved elsewhere — to access and rent out his Baruch Houses apartment, according to a federal complaint.

More than 160,000 families are on NYCHA’s waiting list, and 55,000 tenants are living in pads larger than they’re entitled to, agency chair John Rhea has said.

More than 25,000 single residents are living in two-bedroom units — which require at least three people under federal rules.

At the Martin Luther King, Jr. Towers in Harlem, one tenant who lives alone in a two-bedroom pad posted a Craigslist ad offering a spare room for $500 a month.

“This is not Trump Plaza,” he told a Post reporter who visited the apartment. “You don’t have to have 20 applications. You don’t have a broker’s fee. It’s simple.”

The $500 room has a ­linoleum floor and closet. Utilities are included.

“You’re not the first one here, and you’re not going to be the last,” he said. “As soon as you go, I’m going to find somebody else because I need the finances.”

Meanwhile, other NYCHA residents are turning their government-funded homes into cheap hotels.

Mike Velasquez, 38, who lives in the Alfred E. Smith Houses, has turned his two-bedroom apartment into a hotel — offering a private room or sofa for $50 to $100 per night.

“I don’t care,” he told The Post when confronted about the legality of his rental. “There’s plenty of people who rent rooms — everyone does it.

“I pay my rent. I can do what I want.”

Velasquez’s 13th-floor apartment overlooks the Manhattan and Brooklyn bridges and is blocks from the South Street Seaport. Web sites show that he has been a secret innkeeper since at least 2011.

If he rents out the apartment three days a week, that’s up to $1,200 in extra spending cash a month.